Radio communications system, mobile station, base station, and radio communications method

Abstract

A radio communications system includes a mobile station, a third generation base station that communicates with the mobile station using a 3G system, and a long time evolution (LTE) base station that communicates with the mobile station using an LTE system. The mobile station includes a communication controller and a 3G communication module. The communication controller determines feasibility of communication with the LTE base station using the LTE system. The 3G communication module notifies the 3G base station that the communication with the LTE base station is not feasible at the time of transmitting a communication request to the 3G base station when the communication controller determines that the communication is not feasible. The 3G base station communicates with the mobile station using the 3G system in response to the communication request without requesting the mobile station to communicate with the LTE base station.

What is claimed is: 
     
         1 . A radio communications system comprising:
 a mobile station;   a first base station that communicates with the mobile station using a first communications system; and   a second base station that communicates with the mobile station using a second communications system, wherein   the mobile station includes
 a determining unit that determines feasibility of communication with the second base station using the second communications system, and 
 a notifying unit that notifies the first base station that the communication with the second base station is not feasible at the time of transmitting a communication request to the first base station when the determining unit determines that the communication is not feasible, and 
   the first base station includes
 a communication unit that communicates with the mobile station using the first communications system in response to the communication request without requesting the mobile station to communicate with the second base station. 
   
     
     
         2 . The radio communications system according to  claim 1 , wherein the notifying unit of the mobile station notifies the first base station of a frequency number for the second base station at the time of transmitting a communication request to the first base station. 
     
     
         3 . A mobile station that communicates with a first base station using a first communications system and communicates with a second base station using a second communications system, the mobile station comprising:
 a determining unit that determines feasibility of communication with the second base station using the second communications system, and   a notifying unit that notifies the first base station that the communication with the second base station is not feasible at the time of transmitting a communication request to the first base station when the determining unit determines that the communication is not feasible.   
     
     
         4 . A base station of a first base station that communicates with a mobile station using a first communications system, the base station comprising:
 a communication unit that communicates with the mobile station using the first communications system in response to a communication request from the mobile station without requesting the mobile station to communicate with a second base station when a notice of the communication with the second base station being not feasible is received at the time of receiving the communication request.   
     
     
         5 . A radio communications method in a radio communications system including a mobile station, a first base station that communicates with the mobile station using a first communications system, and a second base station that communicates with the mobile station using a second communications system, the radio communications method comprising:
 determining feasibility of communication with the second base station using the second communications system by the mobile station;   notifying the first base station that the communication with the second base station is not feasible at the time of transmitting a communication request to the first base station when the communication is determined to be not feasible by the mobile station; and   communicating with the mobile station using the first communications system in response to the communication request without requesting the mobile station to communicate with the second base station by the first base station.